The four lads from Down Under may be known as the opening act for the reigning princes of pop, One Direction, but they’re ready to take the crown.

“5SOS” as they’re known to adoring fans — including 11 million Twitter followers and counting — bears an uncanny similarity to One Direction in both looks and music.

But the screaming girls who swarmed Midtown Tuesday armed only with their camera phones and undying devotion are finished with 1D, with eyes only for 5SOS.

Alexis Marineau wouldn’t camp out for two days for just any boy band: “I just really love them. I can get emotional, but I don’t want to,” says the 19-year old from upstate New York who schlepped to NYC two days ago for the group’s concert Tuesday night. It’s the kick off of their first North American tour — making tens of thousands of rabid teen girls ecstatic — and sending millions more who couldn’t score tix into a fit of despair.

She was one of the lucky ones.

Fans Margaret Pepe and Debbie Oyarzin trekked from Long Island to support 5 Seconds of Summer, who are in NYC to play a sold out show at the Best Buy Theatre in Times Square.Christian Johnston

“It sold out in 30 seconds!” laments dejected 14-year old Olivia from Brooklyn. “The scalpers are selling tickets for $1,000 — and they were $20 tickets!”

For 16-year old Domenica from Kenilworth, NJ, even a day stalking — make that following — the hunks around Midtown has been excitement enough. “My mom doesn’t even know I’m here,” she confesses.

“She thinks I’m at the mall — she would kill me if she knew I took the train into the city.”

“I’m playing hooky from work today,” admits “Jane,” an accountant from Centereach, LI, who’s chaperoning her two teen daughters and their two friends. “The girls are playing hooky too.”

Setting out on the 5:30am train to NYC didn’t help them score last-minute tickets to the concert, but it hasn’t tainted the day for Jane and crew, even if they did have to wade their way through thousands of gushing fans. “I haven’t seen hysteria like this — ever,” says the mom.

Like many well-coiffed idols before them, the boys from Oz were discovered after posting a homemade YouTube video in 2011. One Direction’s Louis Tomlinson propelled the heartthrobs to teen idols by saying he was a fan and posting a link. The 5 Seconds of Summer members, Luke Hemmings, Michael Clifford, Calum Hood and Ashton Irwin, are all 17 to 19 years old. Their latest EP (their second), “She Looks So Perfect,” climbed to No. 2 on the Billboard album chart when it debuted on April 1.

This sudden stardom has even taken the guys by surprise.

“We’re average working class boys,” Luke has said. “We come from places where we struggled for money, none of our parents are well-off so we learned to value everything that’s given to us.”

Olivia, 16, from Rockville Centre, LI, knows it’s love, even if her mom isn’t convinced: “My mom said, ‘You’re not going to marry them, so why do you have to see them?’” she recalls outside Sirius Radio where the teen hoped to glimpse the fab foursome.

“I say live in the moment!” The teen, who kept pace with the band’s tour bus from the West Side to the East River, is bummed she didn’t score a pic with them — “their security wouldn’t let them!” — but she understands the stakes: “New York fans are out of their minds.”

Fans swear 5 Seconds of Summer has more edge than their mentors. “One Direction is a boy band, pop,” sniffs upstater Marineau, on day two of camping out by the Best Buy Theater, subsisting on quick Chipotle and Starbucks runs. “But they are more rock.”

And, she adds with a hopeful note, “They don’t have girlfriends — that we know of.”